This invention relates to a device for the generation of auxiliary pressure for slip-controlled brake systems with a pedal-force-operated brake booster connected to a tandem master cylinder. The hydraulic pressure is controlled as a function of thermodynamics state variables of different energy sources.
In known brake systems of this type a tandem master cylinder with a vacuum brake booster connected upstream is used as a braking pressure generator (German Published Patent Application DE-OS 35 05 410). The device for generating an auxiliary pressure consists of a hydraulic pump driven by way of an electric motor and communicating with a pressure medium storage reservoir and an auxiliary pressure control valves. At the wheel brakes directional valves connected to the braking pressure generator are inserted into the brake lines from the braking pressure generator cylinder to the wheel brakes. In their rest position, that is, in their initial position, the directional valves hydraulically connect the braking pressure generator with the wheel brakes. After a change-over into a second operating position, the valves connect the auxiliary pressure source to the brake lines and, therefore, to the wheel brakes. To this end, 2/2-way valves are arranged in tandem in each brake line. Of these valves, the first valve is pressure-operated while the second valve is electrically operated. In each case, a pressure line which is provided with a check valve connects the hydraulic pump with the brake line section. This links the two directional valves thereby to establish pressure medium communication. A return line is connected to each brake line section connecting the second directional valve with the wheel brakes. IN each case a third electrically operated two-position directional valve is arranged in the return line. As the demanded auxiliary pressure generation is ensured by the additional arrangement and the electrical activation of a specifically designed electric drive at the hydraulic pump an additional substantial constructional expenditure is needed in order to guarantee a necessary separate energy source for driving the hydraulic pump.
One of the objects of the present invention is improving a brake system with slip control of the type referred to, so that, while using a simple and cost-saving structural means and maintaining the operational reliability, a device for auxiliary pressure generation is provided. The device ensures the demanded generation of auxiliary pressure without external energy sources at a minimal constructional expenditure and with the advantageous feature of integration into the brake booster.